Enhanced Terminal Mobility through the use of Filters for ... - CiteSeerX

Enhanced Terminal Mobility through the use of Filters for Mobile IP Koojana Kuladinithi, Nikolaus Fikouras, Andreas Könsgen, Andreas Timm-Giel, Carmelita Görg ComNets, Universität Bremen, Otto-Hahn-Allee NW1, 28359 Bremen, Germany {koo|niko|ajk|atg|cg}@comnets.uni-bremen.de

ABSTRACT There are currently, many bearer technologies available (Wireline, WLAN, GSM, GPRS, UMTS, etc.) that modern communication devices can use to connect to the Internet. Mobile IP enables such devices to use any of these bearer technologies even while roaming between them and without breaking ongoing communications. However, Mobile IP does not provide the facilities for mobile nodes (hosts or routers) to concurrently use multiple points of attachment to the Internet, even though modern communication devices may host multiple interfaces. ‘Filters for Mobile IP’ is an extension to the original protocol that allows for the efficient use of multiple interfaces on a single device. This study makes a case for ‘Filters for Mobile IP’, describes its functionality and highlights scenarios where its presence is required. I. INTRODUCTION As mobility is becoming the watchword of our civilisation, the way we communicate, socialise and do business is being revolutionised. At the forefront of this revolution is the Internet. Originating from the Advanced Research Projects Agency Network (Arpanet) of the US Department of Defence it has been witnessing tremendous expansion since early 1990 when the US National Science Foundation (NSF) privatised the network. As the Internet is already approximately doubling in connectivity and reach every year, it is being contemplated to connect any device hosting a computer of any size to a global Internet. It is envisioned that mobile users holding one or more unique Internet addresses will roam between provider networks switching their bearer technology, when necessary, without having to interrupt active communications. Terminal mobility is the term given to the ability of a mobile node to roam between different administrative domains. Terminal mobility was originally not possible in the Internet. As such, mobile nodes escaping the boundaries of an Internet administrative domain (sub network) would have to give up all active communications. Mobile IP is the solution introduced to overcome this problem. Mobile IP [1,2] is an extension to IP that provides continuity of communications through the use of a permanent IP address. Mobile IP inherits the capacity of the Internet Protocol (IP) to operate with disregard for the underlying bearer technology. This makes it possible to roam between homogeneous as well as heterogeneous IP capable bearer technologies (e.g. wirelined, Wireless LAN,

UMTS, GPRS and UMTS). For example, a mobile node may be connected to an Ethernet, but when disconnected and carried around by the user, it would transparently switch to a connection through a high-speed wireless local area network. While moving around within a building, the mobile node could switch transparently from one wireless sub network to another, and when leaving the building, would switch transparently to a wide-area wireless data service such as GPRS or UMTS. The increasing usage of mobile devices such as laptops, Personal Digital Assistants (PDAs) and smart phones, has led to the possibility of accessing Internet and Intranet through a multitude of network bearer technologies [4,5]. As of the writing of this document there exists at least one PCMCIA NIC which supports WLAN, GPRS, HSCSD & GSM on the same card (Nokia D211) while laptops are equipped with built-in wireless and fixed network interfaces. It is considered that the availability of mobile nodes equipped with support for more than one network bearer technologies will empower users to concurrently utilise different points of attachment to the Internet in order to receive the best possible service or to distribute their traffic load. In this paper, the protocol extension named ‘Filters for Mobile IP’ is introduced. It provides mobile nodes, with the means to relay to the network, their wish to handle specific traffic flows in a specific way. This is achieved with the help of filters that identify the flows and the corresponding control information that indicate a specific action. In that manner, it is possible to distribute, drop or handle traffic in any other way at some point in the core network as indicated by a remote mobile node. This extension enhances the traditional view of terminal mobility of Mobile IP by focusing on the improvement of concurrent usage of multiple points of attachment. This introduction is followed by a section that provides an understanding of Mobile IP, while the third section focuses on the operations of ‘Filters for Mobile IP’. The fourth section looks at a few scenarios which explain the possible use cases of Filters for Mobile IP. The fifth section discusses related research. The last section is a concluding summary. II. MOBILE INTERNET PROTOCOL Mobile Internet Protocol (MIP) is an enhancement of the Internet Protocol (IP) that enables a Mobile Node (MN) to move from an IP administrative domain (sub network) to another and yet maintain its active connections. This is

achieved by preserving reachability on a permanently allocated IP address called the home address. Each MN is associated with a unique home network as indicated by its permanent home IP address. Every time the MN acquires a roaming IP address, called Care of Address (CoA), through a new point of attachment, it is required to issue a Registration Request to the respective mobility agent which maintains a record of the MN’s new location. The term Mobility Agent is used to refer collectively to MIP entities such as the Home Agent (HA), Foreign Agent (FA), or Gateway Foreign Agent (GFA) [7]. Once a HA receives a registration request, it is required to make a record of the MN’s home IP address along with the registered CoA. The sum of that information is called a Mobility Binding. Figure 1 illustrates the basic operation of Mobile IP [1,2]. A Correspondent Node (CN) is any potential communication peer of a mobile node. The CN may be either mobile or stationary. In this example, the MN is currently connected to the home network. Once the MN moves to a visiting network, the HA would intercept the packets addressed to MN’s home address, and then forward (tunnel) them to the newly acquired address on the visiting network (i.e. to the MN’s current point of attachment). In this manner, the MN’s movement is hidden to the communication peer (CN) while maintaining connectivity to the MN. CN

III. FILTERS FOR MOBILE IP In general, it can be said that ‘Filters for Mobile IP’ provides two major functions, namely the distribution of active flows and remote firewall management. 1) Flow Distribution: In a multi-interfaced MN environment, ‘Filters for Mobile IP’ allow MNs to distribute their flows among the available points of attachment in an efficient manner. The filtering may occur with a wide range of different criteria such as bandwidth, reliability, QoS or user preference. 2) Remote Firewall Management: The MN can instruct its HA to act as a firewall for specific data flows. ‘Filters for Mobile IP’ enables firewall management functionalities like filtering particular types of communication and disabling route optimisation in order to maintain privacy. In order to support the aforementioned behaviour, a mobility agent needs to be instructed with a set of rules (filtering criteria) by the MN. ‘Filters for Mobile IP’ specifies the types of filtering criteria and the formats of control data that should be communicated between the Mobile IP entities. Filters for Mobile IP introduces the following terms: •

FA

HA

Mobile IP’ is to control the choice of interfaces to use for incoming traffic to a MN. The functionality of this extension is presented in more detail in the following section.

Internet

•

Foreign network Home network

FA

MN

MN

•

MN movement Foreign network

MN

Figure 1. Basic Mobile IP Protocol

In a multi-interfaced environment, one key aspect of a MN is its ability to connect concurrently to the Internet via many points of attachment. In this case, a MN running standard Mobile IP, sends registration requests with the ‘S’ (simultaneous binding) flag set to one. This will result in the mobility agent duplicating all IP traffic to all registered (active) points of attachment of the MN [1]. This behaviour might be appropriate in order to achieve lossless hand-offs but it is a waste of resources when used for normal communications. It can be said that this behaviour of Mobile IP prevents the efficient use of available points of attachment. One of the motivations of ‘Filters for

Filtering Agent: Any mobility agent that manages filtering criteria with its mobility bindings and effects the behaviour as described. Filter Module: A single filtering criteria that specifies the condition to check for filtering IP traffic. Filter: A collection of filter modules.

When a MN attempts to make a new binding with the HA, it sends a registration request. If the MN requires to activate a filtered behaviour, it is required to attach filtering information to the Registration Request. These filtering information are sent as extensions following the Registration Request. Figure 2 illustrates the format of the filtering extensions. FM 1 Registration Request

FM 2

FM

- Filter Module

FMD - Filter Management Data

Filter 1

FM n FMD Filter n

Action Target Index

Figure 2 Filtering extension

As shown in the Figure 2, a Filter may consist of multiple Filter Modules, each of which have an AND relationship between them. When there are multiple filters, there is an OR relationship between filters. Each filter must always be followed by a filter management data set (FMD), which consists of the following instructions. • Action that should be taken in respect to the filters being sent. It can be an add, delete, replace or flush to the current filter list at the filtering agent. • Target operation to perform when the flow satisfies the filtering rule. The target can be accept, reject, drop, etc. • The index of the filter rule being sent. The index is the ordering number of the filter within the filter set. The order implies what priority each filter holds when selecting the path to use for a given flow. If the MN needs to send filters immediately, it can generate a registration request with which the filters can be sent. This can also be done using the refresh registration request sent by the MN to extend the lifetime of the mobility binding. Once these filters are received by the Filtering Agent, it attempts to apply these filters. If any or all filters fail to apply, the unapplied filters are returned with the Registration Reply. Filters for Mobile IP defines different filter modules that consider any of the following filtering criteria [3], • Type of Service • Protocol Number • Source Address • Source Network • Source Port Number • Source Port Number Range • Free form, specifies the value of an area anywhere within the IP packet There exists at least one implementation of ‘Filters for Mobile IP’ that provides support for all the filters mentioned above [6]. Filters for Mobile IP are a set of extensions that are appended to the registration request/ reply messages of standard Mobile IP. Once the filters are notified to the filtering agent, they can be referred to, by their index numbers in order to refresh, delete or flush. In this way, when performing handoffs or when returning to the home network, only FMD type filter extensions are required to be appended to the registration requests/replies. Figure 3 explains the operation of Filters for Mobile IP through the use of an example. This example is a scenario, where a MN with multiple points of attachment requests from its mobility agent (HA) to differentiate the flows among the available points of attachment for the purpose of balancing the incoming load. In this example, the user wishes to have a video conferencing session, browse the web, and retrieve mail simultaneously. The user specifies that the delay sensitive communication like video conferencing traffic (via UDP) has to use the foreign network 2 because of its relatively

better bandwidth, while the HTTP and SMTP/POP3 traffic has to use the foreign network 1. The sequence of required activities is described in more detail in the following: UDP HTTP SMTP/POP

Video Conferencing Partner 1

Mail Server

HA 2

Internet

3

Home network

5

Web Server

4

FA 1

FA 2

Foreign network 2

Foreign network 1

MN

Figure 3 Filtering based on the Protocol Number

MN is connected to the Internet 1 2 3 The MN’s user has initiated the video conferencing, web browsing, and mail retrieval sessions through the Internet connection. MN moves out of the home network and makes bindings through FA1 and FA2 The two connections (to FA1 & FA2) result in two registration requests (as explained in section 2) to the HA. With these registration requests, the MN piggybacks the following filter information, CoA with FA1 is for HTTP, SMTP/POP3 traffic CoA with FA2 is for UDP traffic HA sets up the filters for the CoAs of the MN When the HA receives the filter information, it sets up the routing accordingly, so that the UDP destined for the MN goes through FA2 and the HTTP, SMTP/POP3 goes through FA1. HA routes data according to the filter criteria 4 5 When the MN destined IP traffic is received at the home network, the HA (filtering agent) intercepts them and tunnels them to the FAs based on the filtering criteria.

Registration Request Filter 1

Protocol Type = UDP

FM

Action = Add Target = Accept

FMD

Index = 1

Figure 4 Filtering extension sent to the FA2

Fig. 4 illustrates the data values of the filtering extensions sent to the FA2 as explained in the above example. In the above scenario, the HA acts as the filter enforcing agent. But, the HA is not necessarily required to perform filtering. This could also be done by the Gateway or Regional Foreign Agents which are present with Hierarchical Mobile IP [7]. IV. USE CASES IN FILTERS FOR MOBILE IP Mobile IP and Filters for Mobile IP (explained in sections 2 & 3) form an environment that allows the continuous and concurrent use of all points of attachment provided by a multi-interfaced MN. Mobile IP allows the user to maintain session continuity while Filters for Mobile IP provides the efficient use of multiple points of attachment. This section explains the functionalities of Filters for Mobile IP, with some practical usage scenarios. Flow Distribution:. As explained in section 3, Filters for Mobile IP enables the flow distribution among the active points of attachment, based on user preferences, special services or load balancing, in order to use available networking technologies efficiently. User Preferences: Different points of attachment have different QoS (dedicated bandwidth, controlled jitter & latency, reliability, etc) and cost/tariff (based on duration/volume of data) to be considered. There exists no single bearer technology capable of satisfying the diverse requirements of all services. There is always a trade off between bandwidth, coverage, reliability and cost. User can use Filters for Mobile IP to choose one or more points of attachment according to his/her preferences, based on the above criteria. Special Services: Filters for Mobile IP enables the MN to choose any data field (e.g., packet length, destination port) within an IP packet as a filtering criterion (using a free form based filter). Load balancing: A MN can also distribute its traffic load among its available points of attachment for the purpose of balancing the load. One such criterion would be on a percentage basis, where a certain percentage of IP traffic is sent through one point of attachment.

Selecting the required Sources: This enables the user to either select or block particular flows. This blocking can be based on suitability for the current means of communication or to restrict access. The following scenarios show specific usage situations of Filters for Mobile IP in the areas of Flow Distribution (FD) and Remote Firewall Management (RFM). Scenario-1(FD): A PDA, which is capable of running Mobile IP and Filters for Mobile IP, has simultaneous access to a WLAN as well as UMTS points of attachment. Intuitively, the best way of distributing delay sensitive video traffic is through WLAN, as it has a higher bandwidth and is also cheaper, compared to UMTS. But, if the user is concerned about QoS, he might use UMTS instead of WLAN. On the other hand, if the user is concerned about the cost factor, irrespective of QoS, then he would prefer to use UMTS restrictively or not at all, when having access to a WLAN. Scenario-2(FD): GSM networks have low bandwidth but relatively low latency, while GPRS provides higher bandwidth and higher latency. The user can decide to use low bandwidth flows (such as telnet traffic) which requires low latency, while using GPRS for the data transfer flows which require high bandwidth but do not demand for low latency (such as ftp). Scenario-3(FD): When the MN has two WLAN connections (eg. both 802.11a and 802.11b), the user can select all TCP and UDP to utilize the 802.11a attachment, while HTTP and SMTP can utilize the 802.11b. The purpose of this separation by protocol is simply to balance the load. But, this separation can also be done based on many other criteria such source IP address, source port, etc. or using a combination of these. Scenario- 4(RFM): When a MN is in a coverage area of a very low bandwidth network like a GSM network, the user can decide to block bulk flows (dedicated file transfer, streaming audio & video applications) and to receive only traffic flows which are suitable for current means of communication (SMS, Voice). V. RELATED WORK

Remote Firewall Management: Filters for Mobile IP allows the remote setting of firewall rules for the purpose of privacy and to control different incoming flows.

Research in the area of multi-interface usage on a single MN focuses on different areas of improvement. Following section presents issues and projects related to Filters for Mobile IP.

Privacy: Mobile IP introduces route optimisation in order to optimise the network resources. As explained in the route optimisation in Mobile IP [8], the HA can inform MN’s current location to the CN. If the MN wants to keep its location private, the MN can use Filters for Mobile IP to inform the HA to switch off route optimisation, i.e. not to give its location to the CN.

Filters for Mobile IP & Multi-homing: A multi-homed node is a host having more than one globally routable IP address. These addresses could be on the same or different sub networks. With IPv4, multi-homing is not widely used due to the lack of IP addresses. But, with the address abundance in IPv6, this has become a viable possibility (11). IP is based on the quintuplet which consists of the

source address, source port, destination address, destination port, and the protocol type. Changing one of these entities in a communication session indicates the termination of this session. Filters for Mobile IP can only operate on sessions that do not change this quintuplet while communicating. MosquitoNet Project: The Mobile Computing Group at Stanford University has implemented a network layer solution based on Mobile IP [10], to control the selection of the most desirable points of attachments for both outgoing and incoming packets for different traffic flows. Their work is different from Filter for Mobile IP in the following manner: •

•

Traffic flows are distinguished based only on flow management and considering 3 criteria (MN’s home IP address, the CN’s IP address and CN’s port number). But, Filters for Mobile IP introduces more flexible criteria to differentiate traffic flows and the possibility of combining filtering criteria in many different ways using AND, OR relationships. It enables the remote firewall functionalities as well. ‘Filters for Mobile IP’ has not discussed the differentiation of flows for outgoing traffic. This is considered as vendor specific and this does not fall within the realm of Mobile IP.

BARWAN Project: The BARWAN project [9] at UC Berkeley concentrates on providing low latency handoffs among different points of attachment. It deploys a proxy architecture for each MN that adapts the multimedia format of the transmitted content (high bandwidth video to low bandwidth video), to suit the available resources of the selected point of attachment. This solution ignores the existence of parallel points of attachment that could be used to transfer the original flow. Filters for Mobile IP aims to provide the means for exhausting the available resources prior to adjusting the content. That is, Filters for Mobile IP focuses on utilising all of available points of attachment in an efficient manner, while BARWAN focuses mainly on adjusting the content. VI. CONCLUSIONS Mobile IP is the solution that provides continuity of sessions while being mobile, independent of the bearer technology. In future, IP centric and Internet based mobile computing devices will be capable of having multiple points of attachment which can utilise different network technologies, concurrently. It is desirable to differentiate traffic flows and choose the appropriate points of attachment in a multi-interfaced single host environment. Mobile IP specifies that all IP traffic destined to a mobile node would be multiplied to all the active points of attachment. Filters for Mobile IP is a solution to overcome this problem where the mobile node is able to specify which flows should use which points of attachments for the

purpose of distributing traffic flows and remote firewall management. Filters for Mobile IP is also a network layer solution as Mobile IP. This paper has shown how Filters for Mobile IP is able to extend Mobile IP for multi-interfaced single mobile node environments, by enabling mobile nodes with multiple points of attachment to utilise all of them concurrently, as they see fit. Filters for Mobile IP have been successfully implemented on Mobile IPv4. Publications of a similar extension for Mobile IPv6 are underway. ACKNOWLEDGEMENT This research project has been supported by the German “Bundesministerium für Bildung und Forschung” within the project ‘COVERAGE/MULTIHOP’ and the European Commission within the IST project NOMAD (IST-200133292). REFERENCES [1] C. E. Perkins, IP Mobility Support. Request for Comment (Proposed Standard) 3344, Internet Engineering Task Force, 2002 August. [2] C. E. Perkins, Mobile IP Design Principles and Practices, Wireless Communications Series. AddisonWesley, 1997. [3] N.A. Fikouras, A.J. Könsgen, C. Görg, W. Zirwas, M. Lott, Filters for Mobile IP Bindings (NOMAD).draft-nomad-mobileip-filters-02.txt, IETF, July 2002. [4] I. Guardini, P. Fasano, “The Role of Internet Technology in Future Mobile Data Systems”, IEEE Commun., Vol 38, No. 11, Nov 2000. [5] M. Chiussi, A. Khotimsky and S. Krishnan, “Mobility Management in Third-Generation All-IP Networks”, IEEE Commun., Vol 40, No. 9, Sep 2002. [6] ComNets, University of Bremen, Mobile IP Research & Development, WWW-site (10.2.2003), http://www.mobileip.org [7] E. Gustafsson, A. Jonsson and C. Perkins, Mobile IP Regional Registration. (work in progress), draft-ietfmobileip-reg-tunnel-06.txt, IETF, Oct 2002. [8] C. Perkins, D. Johnson, Route Optimisation in Mobile IP. (work in progress), draft-ietf-mobileipoptim-11.txt. [9] R.H. Katz and E.A. Brewer, “The Case for Wireless Overlay Networks”, in Proceedings of the SPIE Conference on Multimedia and Networking, 1996. [10] Xinhua Zhao, Claude Castelluccia, Mary Baker, “Flexible Network Support for Mobile Hosts”, ACM/Baltzer Journal on Mobile Networks and Applications, 2001. [11] IST-2001-32603, 6net project, Deliverable D4.5.1 “Report on IETF Multihoming Solutions”, Oct 2002, WWW site, http://www.6net.org.